Shop OBEX P1 Docs P2 Docs Learn Events
Multiple power supplies decreasing battery life — Parallax Forums

Multiple power supplies decreasing battery life

UghaUgha Posts: 543
edited 2008-04-12 02:33 in BASIC Stamp
I was just going through my "look this up" list that I add to whenever I see something I don't understand.

It seems that quite some time ago, somewhere, somehow, I ran accross info that said connecting the
grounds from multiple power supplies (a requirement to use more than one power supply if i understand
it correctly) will cause them to drain faster... thus killing a battery sooner than expected.

Since I have no idea where I saw this (most likely somewhere on the forum but the forum's search function
sucks) I have no way of further looking this info up.

Is this true? If so, why does it do this and is there any way to prevent it?

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2008-04-11 12:15
    Untrue statement.·

    Hope you didn't read that, unchallenged, anywhere around here.

    A better search means:

    http://search.parallax.com

    Post Edit -- "Lots" of linear regulators will effect battery life.· For instance, with a 12V battery pack, a 5V 1/2A [noparse][[/noparse]= 2 1/2W] output draws 1/2A from the 12V and·that is 6W total demand (not including current the regulators use in their own operation, small comparatively, but still additive.)· Do that twice and you start to get the point.·

    But, that's not the same as joining circuits powered by one battery pack with those powered by another, by making their returns common.




    Post Edited (PJ Allen) : 4/11/2008 12:36:17 PM GMT
  • Dun-deeDun-dee Posts: 6
    edited 2008-04-11 12:18
    While on the topic of multiple power supplies: Are there ever any problems with tying multiple power supplies of different voltages to the same ground? -thanks
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2008-04-11 12:25
    The only problem is in not making solid connections.· You want to make sure that all of the commons/grounds/returns are solidly brought together.
  • Dun-deeDun-dee Posts: 6
    edited 2008-04-11 12:38
    PJ: Could you please define "solidly brought together"?

    Would there be anything additional to wiring all supplies to the same ground? (not completely clear on the use of the word "solid")

    -thanks
  • allanlane5allanlane5 Posts: 3,815
    edited 2008-04-11 12:44
    A "weak" connection would be one in which the wire was stripped badly, had many broken strands, or was barely held on the screw.

    A "Strong" connection would be one where lugs were firmly crimped onto the ground wires, and the lugs all screwed together firmly (assuming you're using a screw-terminal barrier strip or something).

    It's possible to twist all the ground wires tightly together, solder the wires together, then cover the connection with heat shrink. In this case, you have to be careful that the wires don't 'shift' while the solder is cooling.
  • jmalaysiajmalaysia Posts: 97
    edited 2008-04-11 12:58
    "Ground is ground, the world around" - unknown author
  • Tracy AllenTracy Allen Posts: 6,666
    edited 2008-04-11 15:38
    Issues can arise when multiple power supplies are needed for a system. Tying the grounds together is a necessary but not sufficient cause. One problem can happen when one of the power supplies is turned off, but the other is left on. Say one of them powers a Stamp that is turned off, and the other is a battery that powers a peripheral that is connected to the Stamp inputs. Excess current may find its way through "sneak" paths, the substrate diodes say, back into microprocessor and to ground, and that drains the battery faster than expected. It does not have to happen, but it is something the circuit designer has to keep in mind.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Tracy Allen
    www.emesystems.com
  • UghaUgha Posts: 543
    edited 2008-04-12 02:33
    Tracy Allen: What's the most common way of avoiding this?
Sign In or Register to comment.